This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-192889, filed Jun. 27, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a honeycomb sandwich panel for use in an interior material or a partition material or a structure member of an artificial satellite or a space station.
In the aerospace industry, a honeycomb sandwich panel, which is light and strong, is used as an interior material or a partition material or a structure member of an artificial satellite or a space station. The honeycomb sandwich panel comprises a honeycomb core made of, for example, aluminum, which constitutes a cell portion having a number of cells like a honeycomb. The honeycomb sandwich panel also comprises sheets of a front surface layer and a rear surface layer sandwiching the honeycomb core on both sides thereof so as to cover the openings of the cells.
It is known that the honeycomb sandwich panel is used in an artificial satellite or space equipment as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 11-320724. The front and rear surface layers of the honeycomb sandwich panel are made of, for example, sheets of carbon fiber reinforced plastic (CFRP) or glass fiber reinforced plastic (GFRP). In general, the cells of the honeycomb core are hermetically sealed. The honeycomb sandwich panel for use in the space environment, in particular, must be resistant to a vacuum.
As described in the above publication, when the honeycomb sandwich panel is used in an artificial satellite or space equipment, the pressures inside and outside the cells of the honeycomb core are required to be the same. For this purpose, conventionally, air vents are formed on side walls of the cells, or slits are formed on a surface of the honeycomb core. In a vacuum, the air in the cells goes out through the air vents or slits. With this structure of the air vents in the side walls of the cells or the slits in the surface of the honeycomb core, force does not act in a direction to remove the front and rear surface layers from the honeycomb core by the pressure of air remaining in the honeycomb core.
However, since the honeycomb core has a number of cells, it is a difficult to process to make all the cells breathable. In addition, the front and rear surface layers are formed of a carbon fiber reinforced plastic, which does not have air-permeability. Therefore, if the panel is used in a space environment while air remains in the cells, the front and rear surface layers may be damaged or delaminated from the honeycomb core due to a difference in pressure between the inside and the outside of the honeycomb sandwich panel.
Further, if slits are formed on the surface of the honeycomb core, the strength of the core will be reduced and surface smoothness cannot be maintained. The smoothness of the surface of the honeycomb core may be ensured by using a method of adhering the honeycomb core to a hard surface plate. However, this method requires an additional step, resulting in an increase in cost.
In the case where the honeycomb core is made of aluminum, it is possible to form air vents on the side walls. However, since the air passages connected to the outside are formed on end faced (edge) of the panel, the formation of the air vents is limited by the shape of the end faces. Likewise, in the case where the honeycomb core is made of a carbon fiber reinforced plastic, the formation of the air vents is limited by the shape of the end faces of the panel.
Furthermore, according to Jpn. Pat. Appln. KOKAI Publication No. 11-320724, in order to make a honeycomb core breathable, an epoxy-based resin or a polyimide-based resin is combined with a fibrous base material, thereby forming a very thin fiber reinforced plastic with interstices, and a number of small holes are formed by the interstices in the fibrous base material. It is difficult to produce such a structure. In addition, the mechanical strength thereof is small.
An object of the present invention is to provide a honeycomb sandwich panel, in which at least one of front and rear surface layers of a honeycomb panel is made of a fiber reinforced plastic using a phenolic resin as a matrix so that air permeability can be obtained, thereby providing resistance to a vacuum and high durability even when it is used in the space environment, without a troublesome process for forming air vents on the side walls of the cells of the honeycomb core.
According to the present invention, there is provided a honeycomb sandwich panel comprising a honeycomb core and front and rear surface layers sandwiching the honeycomb core on its upper and lower surfaces, in which at least one of the front and rear surface layers is made of a fiber reinforced plastic using a phenolic resin as a matrix.
With the above honeycomb sandwich panel, the honeycomb core is not breathable but the front or rear surface layer or both are porous and breathable. Therefore, when the panel is used in a vacuum, the air in the cells goes out through the front and rear surface layers. Thus, since no difference in pressure is made between the inside and the outside of the sandwich panel, the front and rear surface layers are prevented from being damaged or removed from the honeycomb core. As a result, the sandwich panel with high durability can be obtained. Moreover, even when the ambient pressure is returned to a normal pressure or increased above atmospheric pressure, since air flows into the honeycomb core, no excessive force is applied to the honeycomb sandwich panel. The honeycomb core may be made of Nomex(copyright), a registered trademark of E. I. duPont de Nemours and Co., Wilmington, Del., for an aramid fiber, aluminum or a fiber reinforced plastic. Since the front and rear surface layers have air passages connected to the outside, the shape of the panel is not limited by the process for forming end faces (edge) of the panel but has a degree of freedom. For example, it is possible to form a panel or a structure member with a closed cross section to improve the torsional rigidity. Thus, the panel or a structure member has (much) more freedom of strength. Furthermore, since no special process is additionally required, the manufacturing cost can be saved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.